The present invention relates to optical image scanners and, more particularly, to solid state magneto-optic chips employed as a light valve in a beam of light operated in a raster-scan pattern to develop an output signal associated therewith.
Magneto-optic chips such as that indicated as 10 in FIG. 1 have been known in at least rudimentary form for some time. Several recent embodiments of such chips can be seen in detail in co-pending applications Ser. No. 320,819, filed Nov. 12, 1981 by B. E. MacNeal and W. E. Ross, titled ALTERING THE SWITCHING THRESHOLD OF A MAGNETIC MATERIAL and Ser. No. 375,327, filed on even date herewith by W. E. Ross, titled METHOD AND DEVICE FOR INCREASING THE DENSITY OF A PLURALITY OF SWITCHABLE MAGNETIC ELEMENTS both of which are also assigned to the assignee of the present invention. Basically, chip 10 comprises a substrate 12 having a film 14 thereon of garnet, or the like, which has the characteristic of being relatively transparent while, at the same time, being magnetizable into and out of the plane of film 14 as FIG. 1 is viewed. The film 14 is etched into a plurality of close adjacent posts 16. Typically, the posts 16 are in a rectangular pattern of rows and columns. Control wires are operably disposed between the posts 16 in the manner shown in simplified form in FIG. 2. For convenience, the rows are labelled R1-R6 and the columns are labelled C1-C6. Each column has a control wire 18 in the horizontal direction and a control wire 20 in the vertical direction associated with it. For convenience, the horizontal, or row, control wires 18 are labelled CR1-CR6 and the vertical, or column, control wires 20 are labelled CC1-CC6.
Referring now to FIG. 2 in combination with FIG. 3, magneto-optic chip 10 can be placed in the beam of light 22 between an image 24 and a light detector 26. Light detector 26 is of the type that produces an electrical output signal on its output line 28 which is proportional to the intensity of the light impinging upon it. Appropriate lenses 30 are interposed in the light beam 22 to pass the entire light beam 22 through the addressable areas of chip 10. A polarizer 32 is placed in the light beam 22 on one side of chip 10 and a polarization analyzer 34 is placed on the opposite side of the chip 10. A driver circuit 36 is operable connected to the wires 18, 20 by cable 38 and also provides a synchronization output on line 40. The film 14 further has the characteristic of rotating a polarized light beam from its entry axis alignment clockwise or counterclockwise, depending on the direction of the magnetization by what is known as the Faraday effect. As is well known, if polarized light is passed through polarizing film with axial alignment, virtually no blockage of the light will occur. By contrast, if a polarized light beam is attempted to be passed through a polarizing film having its axis at 90.degree. to the polarization of the light, virtually no light will pass therethrough. The polarization analyzer 34 is a polarizing film. It is placed in alignment with the polarizer 32 such that polarized light from the polarazer 32 passing through the chip 10 which is rotated in one direction will come into closer alignment with the polarizing axis of the analyzer 34 while light rotated in the opposite direction will be driven further out of alignment with the axis of the analyzier 34. The posts 16 can be individually addressed by the wires 18, 20 in the manner of a computer memory; that is, if proper current flow is provided in wires CC3 and CR1, the post labelled R1, C3 can have its magnetization set in either direction desired without effect on the other posts.
Turning now to FIGS. 4, 5, and 6, it can be seen how a raster-scan pattern can be created using the chip 10 as a light valve. Assuming the chip 10 has all the posts 16 placed in blocking alignment except for the post 16 at position row 1, column 1 (R1, C1), the only light which should reach the light detector 26 is that corresponding to the upper lefthand corner position of the image 24. If the post 16 at position R1, C1 is placed in its light-blocking position and that at position R1, C2 is placed in the light-passing position by an appropriate current flow through wires CR1 and CC2, the light associated with the second position in the first row of the image 24 will be detected by the light detector 26 as shown in FIG. 5. The "open" position can then be moved to the third column of row 1 as shown in FIG. 6, and so forth, in the manner of a normal raster-scan. This is repeated over and over in the manner of such scans.
Such a basic system is not new in the art and, in fact, is disclosed in the British Pat. No. 1,180,334 by Ronald Ferguson Pearson and Herman Frederick Van Heek.
Such a basic approach would be viable and acceptable if the "on" post were transparent and the "off" posts were completely opaque. Such is not the case, however. The amount of rotation (i.e., Faraday effect) is a function of the color of the light and the thickness of the film. As a practical matter, therefore, the chips 10 are a compromise providing sufficient contrast between the "on" and "off" states that a visible and/or projectible image can be created thereby in the manner of a transparency. When used in the above-described application as a light valve for a scanning image detector or as a spatial filter, however, the chip 10 performs substantially as shown in FIGS. 4-6. The single scanning "on" post 16 is virtually transparent but the remaining "off" posts 14 are far from opaque. A significant amount of background or "noise" light will pass through the film 14 of chip 10 even if all the posts 16 are placed in the "off" state. The result is shown in the graph of FIG. 7 which represents voltage versus time. As can be seen, the detector 26 outputs, for example, 10 or 12 volts of DC background light signal while the changes in voltage indicated at 42 from the opening of a single post 16 to the passage of light therethrough is in the millivolt range. This can be understood when one realizes that even a small chip 10 as presently being tested by the assignee of this application is a grid of 48.times.48 posts for a total of 2304 posts. As can be easily calculated, each post contributes only slightly over 0.04 percent of the total area. With a relatively high background level of light passing through the remaining 2303 posts, the single open posts makes little difference.
Wherefore, it is the object of the present invention to provide an image-scanning system employing magneto-optic chips which have a high signal-to-noise ratio.